A little update on the NYC scenery, I'm currently working on the terrain. All work in progress as of now, but you can already see OSM data (motorway, primary, secondary and railroad) and more detailed landclassing.
We still need a lot of custom buildings (the images below do not contain...
You do need to respect the tree. For NL you'd used something like Objects/e000n50/e005n52/....stg. Terrein will go into a similar folder stru.cture (Terrain/.....).
You might find some additional info at http://wiki.flightgear.org/Howto:_Install_scenery#Technical
Nice blogpost Arno! Let me try to provide some quick answers on the questions that you raised:
There is no slew mode, so I had quite some trouble to view my objects after placing.
Right, that's something we lack. You can move the tower-view around though, by clicking in the scenery, maybe...
Arno, just for your information, FlightGear has an active forum, at which you can get any help you might need. At least you'll reach far more FG developers than you'll find here ;)
Btw, does this mean you started to check whether it is possible to use...